Pneumatic control apparatus



March 13, OLAH PNEUMATIC CONTROL APPARATUS 6 Sheets-Sheet 1 Filed May 2,1950 FIGB Gaorge Olah ATTORNEYS March 13, 1956 G. OLAH 2,737,964

PNEUMATIC CONTROL APPARATUS Filed May 2, 1950 6 Sheets-Sheet 2 lGA George, Ola'q ATTO RNEYS March 13, 1956 e. OLAH 2,737,964

PNEUMATIC CONTROL APPARATUS Filed May 2. 1950 6 Sheets-Sheet 3 GeorgeOlah By M r BQMW ATTORNEYS March 13, 1956 s. OLAH PNEUMATIC CONTROLAPPARATUS 6 Sheets-Sheet 4 Filed May 2. 1950 FIG. 4

Ggorge (Nah ATTOQNEYS 6 Sheets-Sheet 5 Filed May 2. 1950 I07 I00 IOFIG.6

George Oh BY ATTORNEYS FIG.5

March 13, 1956 G. OLAH 2,737,964

PNEUMATIC CONTROL APPARATUS Filed May 2, 1950 6 Sheets-Sheet 6 (\NO m Eg S 3 2 3: Q

01 M o 8% S g E E M Q 5* Q 92$ 1, Q2 2 m l\ s] I I 5 Q R LL 2 6% $88 N=rr a k 8 5 8 g 3 m 5 E 644W AT TORNEYS United. States. PatentThis"invention relates to pneumatic control apparatus of that characterwhich when supplied, for example a measuring or like element, with anincoming signal proportional to the'extent to which'the value ofava'riable of a quantity or process to be controlled has deviated 'iroina required value will yield a pneumatic outgoing signal (for utilisationin a pneumatically operated 'r'eg'ulating element adapted to restore thevariable to there- 'qtiiredvalue) composed of three componentsrespectively proportional to the magnitude, time derivative and timeintegral of the incoming signal. Pneumatic control at:- paratus of thischaracter is commonly referred to as a three-term pneumatic controllerand will be so designatel throughout the following description and inthe appended claims. v w

some examples of known forms of such three-term pneumatic controllersare briefly described "in the ,lfdlloiving paragraphs. V I

In afirst'example, a variable mechanical "linkage wlt'h a regulatablemechanical advantage (it) connects a measuring displacement element (forexample a nouraon tube) with a pneumatic pressure regulating element-(5)'consistingforexample of a nozzle andflapper, anus time detivativebellows ('0 is fedthrough a'regula'talile pneu matic resistance 'Zi-)from the pressure regulating are merit b The time derivative bellows,which has a capacity C and may, in some cases, Zbe connected with anadditional air 've'ssel (a) *as a capacitance element, ito give a totalcapacity C1, is connected through= a further pneumatic resistance with atime integral b'ellows (g), which has a capacity Gr and may be*connected with an additional capacitance element "(h giving a totalcapacity Gr, -a difierential feed back linkage (7 serving to con'nectthe bellows (0) and '(-g) with tlre linkage fialy In anotherarrangement, the incoming signal is mpressure (or pressure difierential)"created by a pressure con verter 6k) disposed between 1 the measuringelemen't an'd the e'ontro'ller and having means (1:1) to regul'atetlreratio between the pressure andthe measured quantity, alre signal:a'ctin'g on a signal bellows '(m) or on the bellows of a p'air (m1 andMn), as the case may be. "I h'e remainder of the mechanism issubstantially as set forth in the preceding-paragraph except that thesignal bellows (m or -'mi and me), the time derivative :bellows (:ctl1'e time integral bellows :(g) and the nozzle ('12 act-:on the beam ofa pneumatic :balance, which beam is iunctionally equivalent to tthedifferential feed-back linkage of thc preceding paragraph.

fIn va preferred 'variant of this :arrangement, the apnea- :m'aticpressure .is t converted by means :of a. flexible menibrane or the likeinto pressure of aliqhid which passes through hydraulic resistancesequivalentuto and misplacingthepneumatic "resistances (d) and f) into a:liquidfilled bellows system replacing the b'e1lows';(r)':and=i(tg)previously described and in which .the :air vessel i'capaci trainees:(e) and -,(h) are replaced by equivalentfsprin'gloaded liquid-filledbellows. This variant Z'has advantage that the small crosslsections'which must be employed in establishing pneumatic resistances.and which are inconvenient from a manufacturing and operational .pointof view can be replaced by the verymuch larger cross-sections requiredfor hydraulic resistances 'due .to the much higher viscosity of :theoperating The functional relationship between the incoming and outgoingsignals in these three-term pneumatic controller may be expressed as:

I", ni-X.

where U=Outgoing signal, expressed as pneumatic pressnne difference.

Umsx=Range of outgoing signal.

M =Incoming signal.

--Mmsx =-:Range of incoming signal; I

. K ='l .roportional band expressed as percentage of -the range ofincoming signal.

t=Time.

Ti=lntegral time constant.

Ta=Derivative time constant.

"is convenient to take as the third constantthe matio in all those knownarrangements, the-three 'haracteristic constants, that is, proportionalba'ndK,integral"tinic constant T1 and derivative time constant Tn, areset up in the controller by the following operations:

1. Setting of the mechanical advantage of linkage (a) or' thee'quivalent setting of the regulating means (k1).

2. Setting of the pneumatic resistance '(d) of the equivalent hydraulicresistance =and/orvaryingl theeapacitysof thea'ir vessel (-2) cr meloading'on-theequivaleht spring+loaded bellows. lheproduct 'ofn'theresistance and the capacity C (or 61") yields an =auiiiliary' tiificonstant T1. g

3. :Setting of the pneumatic resistance (1) or 'tlie equivalenthydraul-ic resistance-'a'nd/or varying the capacity ofsthe air -vessel(h) or the loading on 'the equivalent spring loa'de'd bellows. Theproduct otthe "resistance (f -and:th'e capacity 6 (M61) =y'ielrlsanauxiliary constant F2.

'These-three-settings do not give the three 'characterisfic constants of:the control directly bu't interact between each other' in a complicatedfas'hion, the interaction mg also dependent on individual designfeatures of the apparatus.

important object of the present' inventi'on' is to provide an improvedarrangement in a three terni pneumatic controller whereby the settingdial readings may indicate directly the values of the threecharacteristic constants for the control action. A further object of theinvention is :to provide automatie'temperature{compenfiitioneintthosetcases where a aviscous liquid is employe'rl as .the iworkingmedium and has :to How through hydraulic resistances;

lTheimathematical :basisaof-this invention may-bebriflyindicatedaslfollowsz :Itrhas been found that for any constru'ctio'n-o'ftlfteetermzpnenmatic eontroller such as indicatedabove,;thc

a function of the ratio of the derivative time constant and the integraltime constant only, that is to say wherein is again a function of (n)only.

Furthermore, it has been found that the auxiliary time constant T2 canbe expressed as wherein is the same function of (n) as in Equation 2.Furthermore, from Equations 1 and 3 the derivative time constant may beexpressed as According to this invention, in a three-term pneumaticcontroller, the respective regulatable fluid resistances (which havebeen desginated (d) and (f) in the forego- .ing discussion) are eachconstituted by a passage through a valve of the logarithmic type, i. e.one in which a given regulating adjustment of the movable element of thevalve always produces the same change in the ratio between theresistances of the passage before and after the adjustment irrespectiveof the initial position from which the adjustment was made, andindicating means calibrated in values of is provided to indicate thedifierential displacement between the movable elements of the twovalves.

Similarly, the means for attenuating or amplifying the incoming signal,i. e. the means for regulating the ratio between the proportionalpneumatic pressure and the measured quantity, are logarithmicallyarranged that is, if the control element for operating such means isdisplaced or rotated by a predetermined amount, the attenuation willalways change in the same ratio, this attenuation being a measure of theproportional band.

The valves for setting the time constants T1 and T2 may be so arrangedthat their movable elements are adjusted by rotating two face earns, thesame change in the position of the valves creating the same resistanceratios for both valves. The means for separately adjusting the twovalves are arranged so that they may be mechanically coupled ortemporarily uncoupled. If both means are coupled in a certain relativeposition to each other, adjusting both valves simultaneously producesthe same ratio change in T1 and T2 and consequently the ratio remainsconstant so that according to Equation 1, (n) also remains constant. Ifthe two adjusting means are uncoupled and the one is moved relative tothe other, the ratio of T1 to T2 and hence the value of u change,theextent of the change being determined by the displacement of the onevalve relative to the other.

In accordance with another feature of this invention, a dial. isprovided on the movable element of one of the valve members, or on theoperating mechanism therefor, and a corresponding index is mounted onthe movable elementof the other valve member, or on the operatingmechanism therefor, to co-operate with the dial which latter is thuscapable of indicating directly the value of n which is one of thecontrol characteristics.

Various other features of the invention and details of construction willappear from the following description taken with reference to theaccompanying drawings, where- Fig. l is a diagrammatic representation ofthe elements of a three-term pneumatic controller which has. beenselected as a representative example of the known arrangements, showingthe pneumatic and hydraulic circuits which are utilised;

Fig. 2 is a front perspective view of a practical construction of themain portion of a controller such as is illustrated diagrammatically inFig. 1 but modified by the incorporation of the features of the presentinvention thereinto;

Fig. 3 is a side elevation of the apparatus shown in Fig. 2 with thepressure converter removed, the view being taken from the left of Fig.2;

Fig. 4 is a plan view of the apparatus shown in Fig. 2;

Fig. 5 is a front elevation of the setting dials of the apparatus;

Fig. 6 is a fragmentary section taken on the line VIVI of Fig. 4;

Fig. 7 is a sectional elevation taken partly on the line VIIA-VIIA ofFig. 4, and partly on the line VIIBVIIB of Fig. 4, the adjusting carnsbeing shown in another position corresponding to that indicated inchain-dotted lines in Fig. 4, and

Fig. 8 is a fragmentary sectional elevation illustrating a modifiedarrangement of the dials employed to set the position of the cams.

Referring firstly to Fig. l, the known arrangement diagrammaticallyillustrated comprises an electric lead 1 through which an electricsignal is transmitted from a measuring instrument adapted to respond toa deviation from a desired value of a variable of a process to becontrolled, the magnitude of the signal being proportional to the degreeof deviation. The lead 1 is connected to an attenuating device, composedof a potentiometer shown at 2, which is adapted to be set in order todetermine the ratio between the signal passed on thereby and the actualdeviation measured by the measuring instrument, i. e. to determine theproportional band of the controller. The signal output from theattenuating device is conveyed by an electric lead 3 into anelectro-pneumatic converter 4, the function of this apparatus being toproduce a pneumatic pressure differential proportional to the electricsignal fed into the same at 3. The main pressure supply to the converteris by way of the pipe 5 which is branched from a pipe 6 in the length ofwhich is located a filter element 7. The pipe 6 is supplied at 8 with agaseous fluid under a predetermined pressure which is held substantiallyconstant, for example, at any selected value between say 3 and 20 lbs.per square inch. The pressure of the gaseous fluid supplied at 8 may beindicated on a pressure gauge shown at 9. One of the two pressuresconstituting the output from the converter is conveyed through a pipe 10to the interior of a flexible bellows 11 whereas the other of the twopressures is conveyed through a pipe 12 to the interior of a flexiblebellows 13. Each bellows, 11 or 13, has its one end fixedly mounted andits other end secured to the appropriate arm of a beam 14 pivoted at 15.Upon a change in the signal received at the converter 4 the respectivepressures in the bellows 11 and 13 will be varied to cause tilting ofthe beam 14 about its pivot 15. This tilting motion is utilised todetermine the effective static pressure in a further gaseous fluidcircuit which derives its supply from the output side of the filter 7through a pneumatic resistance which is illustrated as a restrictedpassage 16. The further circuit comprises a pipe 17 leading from thepassage 16 into a further pipe 18 having its one end fitted with anozzle 19 disposed with its outlet directed upwardly against theunderside of "through a pipe '21 from the pipe 6 andis supplied, altertheoneend of the beam 1% and in such close proximity thereto thatvariations in the tposit ion-ot tlre beamaeletive to the nozzle willcorrespondingly vary the degree of freedom with which the pressure fluidmay escape from thepipe' system 17, 18. 'Due to the provision ofaherestricte'd assage 16, therefore, the'static pressure p'r in'g inthesystem 17, 18 at any timewill be-a tune l the deflection of the beam 14and will, "hence, have a o'rhponen t proportional to the pressuredifierential' supplied by the converter 4 as well "as othercornp'onentsderived in the followin manner. The static pressure prevailing in the pie 18 is utilised in a pilot valve 20 of =known e'on- 's'tru'cti'o'n tocontrol the ressureat whichafu'r ther streain of gaseous fluid will nowthrough the pilotval vt't, s'u'ch manner as to ensure that the outputpressure of the fiuid stream will always be functionally proportional tothe static pressure prevailing in the pipe 18. The stream of pressurefluid which is thus controlled is derived pressure-regulation, through apipe 22 from which a branch pipe 23 leads to a transfer device by means"of which thegaseou'sfluid pressure prevailing in thepi e 22 isconverted into a proportional hydraulic pressure of a liquid. Thegaseous fluid under pressure flowing; through the pipe 22 is supplied'to a pneumatically operated regulating device (not shown) which isthereby actuated to modify a condition or conditions in the process to"be controlled in such a sense as to restore the variable of the process"towards the desired value from which it has deviated. A pressure gaugeis preferably arranged inthe pipe 22 so that the pressure prevailing inthat pipemay be indicated continuously. if

The transfer device referred to" comprises a vessel 25 havin itsinternal spacesubdividedby "means 'o'f a fiexi'ble bellows 26 into a,gas space 27 and 'asp'ace'28 filledw'ith a li uid such 'as oil. Thepipezz opens through a wallet "the vessel 25 into the gas space 27 and apipe 29 opens through another wall of the vessel 25 intoft'he'liquidfilled space '28 within the bellows'ze. It will be nn derstoodthat the pressure exerted upon the oil or other liquid contained withinthe bellows 26 will at all times be closely roportional to the pneumaticpressurewhich prevails within the space 27. It will further beunderstood that an increase in the pneumatic pressure will cause liquidto tend to flow out from the space '28 within the bellows by way of thepipe 29. The latter leads through a regulatable hydraulic resistance,constituted by an adjustable valve, indicated diagrammatically at 30, toa pipe 31 which is connected to both a pipe 32 and a pipe 33. The pipe32, in turn, leads to the interior of a flexible bellows 34 having itsone end fixedly mounted and itso'ther end secured to the underside ofthat arm of the beam 14 to which the bellows 11 is secured on the upperside. A capacitance bellows- 35 :has its interior ,placed incommunication with the pipe 32 by way of a branch .pipe 36, "thisbellows being subjected to a predctermined pressure produced by-springloaded means 37 actingfagainst afixed abutment 38. I

The'pipe 33 leads through a second regulata'ble hydrau lic resistanceconstituted by an adjustable valve, indicated diagrammatically at 39 toa pipe '40 which, in turn, leads to the interior of a flexible bellows41 :having itsone end fixedly mounted and its other end secured to theunderside of that arm of the'beam 14 to which the bellows 13 is securedon the upper side. A-capacitance "bellows 42*has-its interior placed incommunication with the pipe-4'0 by way of a branch pipe "43, this'b'ello'ws being spring-loaded at 44, 45 inthe same manner asthebellows'35. I

As' ha's been indicated by the theoretical discussion given above, theproduct of the-total capacity of thetwo bellows 34 and'3i5 and thepreset resistanc'ebifered b'y-"the valve 30 'yields "an auxiliary timeconstantTr while tlreipremet 'Bf the t'otal 'CdPflCitY 'Of the W0Family's-41 8113 42 954 1156 "iliany -trimeeonstant T2; Moreover, theratio is a function 'o'ftheiatio ofthetlerivative time constant Taa'nd'the' integral time constantTr only, and the time constants T1 'andT2 are in practice determined 'bythe settings or the-valves so'and39,respectively.

Consequently, the pressure which builds up in the bell'o'ws 3 4, at arate determined by a correct setting 'of the constant T1, ensures thatthe staticipre'ssnre in the pipe is will contain (in addition to "thecompo ent already referred-to above.) a component roportional tothe"derivanve time constant of the in ut signal, whereas thep'ressure whichbuilds up in "the bellows 41, at a rate determi'nedby acorrect-setting'or the co'n's't'ant T2, ensures that the static pressureinth'epipe '18'wil1 lsb contain a coinponent inversely proportional tothe integral time "constant-oitheinputsignal.

These three-term controllers are known and "farther description of theoperation of the example given is thereforethought'tb be unnecessary.

As has been mentioned in the foregoing, the setting upo'f these 'knowncontrollers is largely a matter of trial and-corre tion or error becauseit is not possible with th'ein to adjust the 'sett'inglcontrolsdirectlyto the respective values of the characteristic constants of thedesired confrdl action, these constants, of course, being capable ofcalculation, by mathematical analysis or from experimental data;consequently, the determination of the values Of the C'O'hStal'ltS fO'lwhich the c'6l1tif0ll1 is 'St involves "computation and anexact-knowledge OfthCfSflV- eral operating constants of the apparatusand the manner in whih a change in each of these reacts upon each of ears.

This diflic'ulty is overcome by the means of the present invention"which make it possible s'oto calibrate thes'etting dials that therespective values of the characteristic constailtsf for which thecontroller is set, or to beset, are dire'ctlyin'dicated. v I

In accordance with the invention, as applied to the contro'lle'rshown"in Fig. 1, the valves 30 'a'ud 39 are ach constructed as a logarithmicvalve wherein the displacement orrotation oi -a movable controllingelement varies the resistance offered to the passage of a liquid throughthe valve and wherein the ratio between the resistances ofiered beforeand after a given displacement or rotation of the controlling element isalways the same irrespective of the initial position from which thedispIaceinen or rotation was effected. In addition, means (notindicatedin the diagram of Fig. 1) is rovided in ssociationwith the twologarithmic valves whereby the difierritial adjustment of the controllinelements'or these valves the be indicated directly, this indicatingmeans being calibrated values of the ratio of the derivative timeconstant (Td) of the signal supplied at 1 to the integral time constant(Ti) of this signal. It will be understood, from the discussion of themathematical basis of this invention, that adjustment of the valve 30will vary the settingof the auxiliary time constant Ti while adjustmentof the valve 39 will vary the setting of theauxiliary time constant T2.The means 'for separately adjusting the two valves-are arranged so thatthey may be rigidly coupled together for actuation in unison after theyhave been set'fin relation to each other, with 'the aidof the indicatingmeans calib'rated in values of Ta Ti ino'rc'le'r todete'rmine-there'quired ratio of the auxiliary tinieeonstants and hence of the valueof n. When so coupled together simultaneous adjustment of the valvesdoes not affect this value of n because the same ratio changes in theresistances offered by the two valves are thereby produced.Conveniently, the indicating means referred to comprises a dial securedto the actuating means for the one valve (that determining T2) and aco-operating index secured to the actuating means for the other valve,the dial being calibrated in values of n which is one of the controlcharacteristics.

The dial secured to the means for adjusting the valve 39 (i. e. fordetermining the auxiliary time constant Tz) is provided with an index toco-operate with a further dial calibrated in units of time and furtherprovision is also made, as hereinafter more fully described, whereby theintegral time may be read directly whether the derivative time be zeroor not. In addition, because a change in the setting for the derivativetime constant requires a corresponding change in the proportional bandsetting, means is provided whereby the potentiometer 2 is automaticallyadjusted as required, all as hereinafter more fully described.

Referring now to Figs. 2 to 8, it will be seen that a convenientpractical construction of a three-term pneumatic controller, adapted tofunction on the basis already described with relation to Fig. 1 butembodying the means of the present invention comprises a compactassembly of the several bellows (marked 11, 13, 34, 41, 35, 42 and 26 inFig. 1) together with the valves (marked 30 and 39 in Fig. l) forcontrolling the regulatable hydraulic resistances, the potentiometer(marked 2 in Fig. 1) and the electropneumatic converter (marked 4 inFig. 1).

The controller comprises a main block 50, 50a and 50b which is ofsubstantially U-shape in plan view (see Figs. 2 and 4) and supports onits upper face, by means of pillars 51, a top plate 52. The centralportion 50 of the block is formed with a downwardly projecting valvehousing 53 (Fig. 3) on the underside of which there is centrally mounteda longitudinally bored support 54 disposed with its axis in thefront-to-rear direction, ball bearings 54a being secured in the ends ofthe bore to carry rotatably a shaft 55 which connects and forms thepivot for front and rear limbs of a rectangular frame 56. This frameconstitutes a balancing beam with equal arms. At the left-hand end ofthe front limb of the frame 56 is secured the lower end of a bellows 57the upper end of which is secured to the underside of the correspondingportion 50a of the block. A. similar bellows 58 is mounted on theopposite end of the front limb of the frame 56 and has its upper endsimilarly secured to the corresponding portion Sill) of the block 50. Atthe lefthand end of the frame 56, on the rear limb, there is secured thelower end of a bellows 59 having its upper secured to the underside ofthe block portion 590. At a similar disposition on the other end of theframe 56 there is secured the lower end of a further bellows 60, theupper end of which is again secured to the underside of thecorresponding block portion 50b. The bellows 60 does not appear in Fig.2 but its location is clearly evident from Fig. 4. The bellows 57 and 58are of such relative sizes and so spaced from the axis of the shaft 55that equal pressures within them will produce equal moments about thisaxis. Similarly equal pressures within the bellows 59 and 60 will alsoproduce equal moments about the axis of the shaft 55.

Reference to'Fig. 4 will show that the bellows 57 may be supplied with agaseous fluid under pressure through a horizontally extending bore 61opening, at its outer end, through the left-hand edge of the blockportion 50a and intersecting, at its inner end, a cylindrical recess 62formed from the underside of the portion 590. Similarly,

the bellows'58 may be supplied with a gaseous fluid under pressure byway of a horizontal bore 63 also opening at one end into the same edgeof the block portion 50a and communicating at its other end with a bore64 formed from the front edge of the block portion b to intersect acylindrical recess formed in the underside of the block portion. Theouter end of the bore 64 is closed by a plug 66. As will be appreciatedfrom a consideration of Fig. 1, the supplies of pressure fluidintroduced into the bores 61 and 63 are derived from an electropneumaticconverter. Such a converter is indicated generally at 67 as mountedcentrally upon the top plate 52 and preferably is constructed inaccordance with the invention forming the subject-matter of co-pendingapplication Serial No. 149,050 filed March 11, 1950, now Patent No.2,669,247. The pipe connections from the converter to the bores 61, 63are omitted for the sake of clearness as also are the electricalconnections to the converter.

On the upper face of the block 50, 50a, 50b, substantially directlyabove the bellows 59, is secured the lower end of a capacitance bellows68 which is subjected to the pressure of a loading spring 69 guided on abolt 70 secured at its upper end in the top plate 52. At the oppositeend of the block there is mounted upon its upper face, substantiallydirectly above the bellows 60, a further capacitance bellows 71 which issimilarly loaded by a spring 72 guided on a bolt 73.

The interiors of the bellows 5'9 and 68, as can be seen from Fig. 4, arein permanent communication with each other by way of a vertical bore 74formed through the block 50, while the interiors of the bellows 71 and60 are in permanent communication with each other by way of a verticalbore 75 formed through the block 50. From the front face of the valvehousing block portion 53 there are formed two valve-receiving recessesof generally cylindrical form but of different lengths, the shorter onebeing marked 76 and the longer being marked 77. Within these recesses 76and 77 there are located logarithmic valves which will be described morefully hereinafter with reference to Figs. 6 and 7. The ports andpassages which are controlled by the operation of these valves areindicated in Fig. 4 and comprise a vertical bore 78 which opens, at itslower end, into the inner end of the recess 76 and, at its upper end,into a shallow cylindrical recess 79 formed centrally of the upper faceof the block portion 50. Within this recess is secured the lower end ofa pressure transfer device which comprises a bellows 80 secured at itsopen lower end to a ring 81 and closed at its free upper end by a disc82 having a central re-entrant portion. Surrounding and slightly spacedfrom the external surface of the bellows 80 is a cylindrical wall 83which is secured, at its lower edge, in an air-tight fashion to the ring81 and, at its upper edge, also in an air-tight fashion to the top plate52. The ring 81 is held in position by a clamp ring 84 and beds upon anelastic sealing ring 85, as shown. When the apparatus is in operation,the space surrounded by the wall 83 and external to the bellows S0 issupplied with a gaseous fluid under pressure by way of a pipe connection86 (see Figs. 2 and 4), whereas the space within the bellows is filledwith a liquid medium. Any liquid which flows through the bore 78 passesthrough the valve mechanism mounted in the recess 76, at a ratedetermined by the setting of the valve, and leaves the recess by way ofan inclined bore 87, the lower end of which is visible in Fig. 6 and theupper end of which opens through the upper face of the block portion 50awithin the boundary of the bellows 68 in order that the liquid, havingpassed through the recess, may be delivered to the interior of thebellows combination 68, 59, A further inclined bore 88 is formed throughthe block portions 50a, 50 with its upper end also located within theboundary of the bellows 68 and its lower end opening through the wall ofthe recess 77. Any liquid which flows through the bore 88 passes throughthe recess 77, under the control of the valve mechanism housed therein,and emerges therefrom by way of an upwardly inclined-passage 89, theupper end of which opens through the upper surface of the block portion50b within the amt-e04 boundar y 'ofthebellows' '71 :so that liquidsupplieddhrongh the torch) will pass into the internal spaceot 'thebellows combination 7 1, 60. A further vertical bore 90 is formedthrough the block to establish communication between the "interior ofthe bellows and the rear end of the recess 77.

It will be "apparent from a comparison-of Fig. l with the constructionsofar described with relation to Figs. 2 *to'7, "that the bellows 8'0-corresponds with that marked 26 in Fig. '1, thebellows s l 'corre'spondswith that marked '13 in 'Fig. 1, thebe'llows 58 corresponds with thatmarked "11 in Fig. l, the bellows "59-'and =60 respectivelycorrespend"to-"those-marked 34 and 41 in Fig. 1, and that thecapacitance bellows 68 and 71 respectivelycorrespond to thoSenra-rkedSS' and 42 in Fig. '1. Moreover, it will be seen from aconsideration of the passages formed in the block "50, SSthat'theseseveralbe'l-lows are interconnected in the manner shown in-the diagram.

Within the recess 76 there is disposed a logarithmic valveassembly-which will now be described with reference to' Fig. *6. Theassembly comprises a hanged sleeve 91 which is a close fit within therecess '76-and is secured in position by rneans of its flange '92. Theinner end or 'thesleeve 91 terminates short of the closed end of therecess76 sothat liquid-flowing through the bore IS-may gain-accessto theinterior of the sleeve. At a-point spaced somewhat from its inner end,the sleeve is formed with an external annular groove 93 solocated thatit will reg- ?ister with the end of the bore 87 formed in the part 53.

The sleeve is also termed with an internal annular groove 94 at the sameaxial location as the groove '93 and" radial =bore95 are formed throughthe thinned wall portion thus left inorder to -establish communication"between the iinrernal and external grooves; The movable element of thevalve, which is adapted to regulate the free cross-sectional arearnade'available for the "flow of liquid ifrom the rear end ofnhe passagethrough the sleeve '91 Iintothe internalannular groove 94, isconstituted by a plug 96which is=a close sliding fit in the frontportion of. the bore through at-he sleeve and .has itsinner end formed,at 97,;vvifl1 controlling .suriiaceszformed :in accordance with alogarithmic curve. The plug 96 is shown :in lEigzstS in outermostposition in which the minimum resistance is oireredito' the'fiow ofliquid to the ports95, :tlie plugtin' this position bearing'iby ashoulderi98 against imam-ruler retaining'p'late :99 which is secured'oversthe mouthof the bore ithrough the"sleeve'91. 'Outwardly ofrhewslroulderv98 the .plug is connected by a :spigot and Socket joint toa coaxial cylindricalstem 100 carrying enlarged v head 101, acompression spring 102 being disposcdauoundlthe plug: and stembetweenwthe inner-surface of the head 101 and the outer surface of theplate Betwcensthe outer periphery of the inner surface of fleewhead10.1:andithednner peripheryofa ring 1 03=WhiCh isr'secunedwto'thcrfiangcl92 on the "sleeve 91 is arranged a .flexiblcfibellows-1'04which'iis' scoured at its ends in .liquiditight sfiashion-totherespective-elements :101 and'103. Betweenfithe latter and the flange 92is interposed a suitable sealingming 195. 'Iihe annular space withinthebellows: tlMais placedin permanent communication with the space art-theinner end of the recess 76 by way of a diametral bore 106 -iand an axialbore 107 formed" in the plug 96. It will be understood that the spacewithin the bellows 104 and the bores1106, 107 are normally filled withthe liquid medium and that the bellows constitute ,an. efiective:liquid-tight sealing :means for the front end o f the valve.

,Astheadjustment -ofathe valve plug 96 .for setting purposes wouldresultin a variationrin the volume oft-the spacewithinrtthe-bellowsllm thebores 106, 107 are ;providedlto ensure that the liquid which wouldthereby be displacedmayireturn to, or be' supplied fromgithe bodycontainedJi-n 'the'bellows 80. In this way, and

deu variarions in'the:pressuresin the lhyclraulic'systemrof thecontroller are prevented.

in "the -front or "outer face of the head 101 there is formed acylindrical recess 108 from the base of which aib'ore 109 'is formedaxially of the stem 100. Acy lindrh cal floating rnernber lull-isprovided with a forwardlyprojectingutemlll in the free end of which isrotatably mounted "a ball 112 "and with a rearwardly projectingcylindrical stem 1 13 which is :a close sliding fit in the bore 109formed in the stem 1 00. The floating nrembe'rdli), on the other hand,isare'latively loose ifit in thecylindrical recess 108 the relativeaxial lengths of the several parts being such that the member largelyprojects from the open endof the recess 108 while the inner end'of firestem 113 is spaced from the closed end of the bore 109. Aroundthemouthofithe recess 108 is formed ianannular groove 11:4 and atecorresponding location on the :memher 110 thereis vformed acomplementary groove 11 5. A ring 1 16 of -a flexible, elastic materialsuch, for example, as rubber, has-its. inner periphery received as atight lit in the groove 1-1-5- and its outer periphery received as atight fit in the groove 114. The free annular space 'thusse'alcd offfrom the external atmosphere, and comprised between the wall of therecess 108 and the stem 113,, is placed in communication with the freespace behind the end of the stern 113 by Way of diametral and axialbores 117and118 respectively formed in the stem 1 13. Through the wallof the head 1101 there is formed a bore to receive a small tube 119, theend of which projects somewhat from the head. By means of this tube thespaces within the head are evacuated and then filled with a suitableliquid, for example, the same liquid as is employed in :the hydraulicsystem of the controller. The outer end of the tube .119 is then sealedas is indicated at 120. Due to-the arrangement described, a rise intemperature will cause zacorrespond-i-ng expansion of the body of liquidcontained within the head with an appropriatedisplacement of. the member110 outwards relative to the head .101. In consequence, the efiectiveoveralllength of the movable element of the valve will be slightlyincreasedso that if theball at the free end of thestem 111 has been setand held in an adjusted position, the plug 96 will beuforcod va shortdistance farther inwards in the bore through the sleeve .91 with anappropriate slight reduction in the .free cross-sectional .area for theflow of liquid from the bore of the sleeve into the ports :95. it willbe seen that the slight reduction in the viscosity of the liquid whichfollows .a rise in temperature will thus be compensated. The arrangementat the head of'the valve plug therefore constitutes an effectivetemperature compensator.

Referring now to Fig. "7,, it will be seen thatthe valve assemblymounted in the recess 77 .has many points *of similarity to that shownin 'Fig. 6, particularly so far as the plugwiththe temperaturecompensating and liquid sealing devices are concerned and correspondingparts-in the two figures are therefore indicated by correspondingreference numeralswith theadd-ition of an index to those which applytothe valve shown in Fig. 7.

The points of difference will now be referred to and it Willbe seen thatthe sleeve 91 has been extended-at .121 to provide acy'lindrical bore122. Between the end of the sleeve proper 91" and the extension piece121, there is formed anlannular groove 123 which is placed incommunication with the interior of .the sleeve by way of radial ,ports124', Secured in a counterbore in the free inner end o'f'the plug 96'is-a headed stud 125 formed with. an axial bore 126 and serving to holdin place an annular piiston127 which is a close sliding .fit in the core122.

128-indicates a spacer collar and 129 a packingor sealing ring.

The external-annular groove ,93 vformed in the sleeve 91' is arranged toregister with the lower end of the-bore 88 formed in the block 50, 53.Consequently, fluid is supplied-from the bellows combination 59', 68 tothe interior of the sleeve 91' under the control of thelogarrithmicallyclrapedsurfaces 97' on the plug 96'. The

1 1 liquid which thus flows through the annular space between theinternal surface of the sleeve and the external surface of the skirtportion of the piston 127 flows out through the radial ports 124 and theexternal annular groove 123 into the inclined bore 89 through which itgains access to the interior of the bellows combination 60, 71.

As before, the space within the bellows 104 is filled with the hydraulicmedium but in this case as the interior of the sleeve 91' must bemaintained isolated from the interior of the bellows 80, any liquidwhich is displaced from the interior of the bellows 104 will flowthrough the bores 106', 107 and 126 to the portion of the bore 122 inthe sleeve extension 121 which is beyond the piston 127. The rear end ofthe bore 122 is in free communication with a clearance space 130surrounding the extremity of the extension 121 and in permanentcommunication with the space within the bellows 80 by way of thevertical passage 90 which has already been referred to. In this way, anydisplacement of liquid from the bellows 104' which may be occasioned bymaking a change in the setting of the valve plug 96 will be preventedfrom causing a disturbance in the pressure conditions within the bellowsarrangements 59, 68 and 60, 71 of the controller. It will be understoodthat the temperature compensating arrangement will function in the samemanner as in the case of the valve already described with reference toFig. 6.

The control adjustment of the plug members 96, 96' of the two valvearrangements is effected in the example illustrated by means of facecams. There are two such cams marked 131 and 132, the outer cam 131being formed on the periphery of a disc 133 which carries aforwardly-projecting tubular portion 134 that is rotatably received as aclose fit in an aperture in a panel 135. The inner cam 132 is alsoformed on the periphery of a disc shown at 136 and this disc carries aforwardly-projecting spindle 137 which is a close rotary fit in thepassage through the tubular portion 134 but extends somewhat beyond thefront end thereof. Around the opening in the panel 135 there is secureda bushing 138 to give greater guidance to the tubular portion 134 andformed with an external annular groove 139 into which may be clipped aspring-retaining ring 140 in order to prevent the return over the freeend of the bush 138 of a dial 141 which is rotatably mounted on theinner end of the bush.

A second and somewhat smaller dial 142 is secured by means of screws 143upon the outer end of the tubular portion 134 formed in one piece withthe cam 131. In addition, an actuating knob 144 is secured upon theouter or forwardly-projecting end of the spindle 137 by means of a key145. It will be seen that normally the dial 141 is rotatably relative tothe dial 142 and knob 144 and that the latter is in turn rotatablyrelative to the dial 142. In order, as is desired, during thefunctioning of the apparatus, to be able to adjust both valvessimultaneously, means is provided whereby the knob 144 may be clamped tothe dial 142. This means comprises a screw axial bore 146 formed fromthe free end of the spindle 137 and a clamping screw 147 engaged in thethreaded bore. By tightening the clamping screw 147, the knob 144 andthe cam disc 136 are drawn tightly' together to be clamped against thecorresponding faces of the dial 142 and the cam disc 133. Should theknob 144 be adjusted with the parts in this condition, the dial 142 willrotate therewith and the two cams 131 and 132 will rotate in unison.

The cam and dial assembly is located with its common axis disposedsubstantially midway between the axes of the two valve assemblies and sothat the ball 112 will be contacted by the operative face of the innercam 132 while the ball 112' will be contacted by the operative face ofthe outer cam 131.

Directly above the cam assembly just described is mounted thepotentiometer which corresponds to that shown at 2 in Fig. 1. Thispotentiometer comprises the usual winding co-operating with a wiper armand disposed within a stepped cylindrical casing 148 which is supportedon its bearer members 149 which project forwardly from the front face ofthe block 50. The arrangement is such that the casing 148 may be rotatedbodily upon its bearer members. At the front end of the neck portion ofthe casing 148, there is secured a toothed gear-wheel 150, the teeth ofwhich are in mesh with those on a toothed quadrant 151 which is securedas by screws 152 to the rear face of the dial 141, it passing through anelongated arcuate slot 153 formed in the panel seeing that thegear-wheel is located at the rear of the panel and the dial 141 islocated in front thereof. The spindle 154 which is adapted to operatethe wiper of the potentiometer extends into and is secured to anoperating knob 155 disposed in front of the panel 135 and rotatablyengaged by its inner end in an aperture 156 in the latter. This knob hassecured thereon an index or pointer 157 which cooperates with acalibrated scale 158 mounted on the front face of the panel 135.

Referring now to Figs. 2 and 5, it will be seen that the scale 158 isgraduated from .2 to 200 and marked Proportional Band Percent.Furthermore, it will be apparent from the nature of the markings on thescale that the potentiometer winding is such as to give a logarithmicrelationship between the adjustments of the pointer 157 and the changesin the ratio between the input signal (referring to Fig. l) and thesignal actually fed to the electropneumatic converter 67.

It will also be seenthat the knob 144 carries an index 159 which isadapted to co-operate with a scale 160 carried on the front face of thedial 142. This scale is graduated from 0.2 to 0.005 and bears theindication Ta/Ti. On the periphery of the dial 142 there is an index 161which is adapted to co-operate with a scale 162 applied to the frontface of the dial 141. This scale is graduated from 200 to 0.2 andcarries the indication Tr.

There is also carried on the periphery of the dial 141 an index 163which is adapted to co-operate with a short quadrant scale 164 appliedto the front face of the panel 135 just beneath the lower portion of thedial 141. This scale is graduated from 0.2 to zero and bears theindication T dTi.

It will be clear from a consideration of Fig. 5 that all the scales areof the logarithmic character.

The potentiometer within the case 148 constitutes the means forattenuating or amplifying the incoming signal and, as has been stated,is logarithmically arranged, that is if the control knob 155 is rotatedby a predetermined angular amount the degree of attenuation before andafter the change in setting will always bear the same ratio, thisattenuation being a measure of the proportional band K.

The plugs 96 and 96 of the valves for setting the time constants T1 andT2, respectively, are displaced by rotating the two face cams 132 and131, respectively, the same change in the position of the valvescreating the same resistance ratios for both valves. If the knob 144 andthe dial 142 are coupled in a certain relative position to each other bymeans of the clamping screw 147, both plugs 96 and 96' will be displacedsimultaneously by ID- tation of the knob and dial to produce the sameratio change in T1 and T2 and consequently the ratio remains constant,so that according to Equation 1, n also remains constant.

If the knob 144 and dial 142 are uncoupled and the one is moved relativeto the other, the ratio of T1 to T: and hence the value of n change, theextent of the change being determined by the displacement of the knob144 relative to the dial 142. The consequent adjustment of the index 159relative to the scale 160 enables the direct reading of the value of n(or Td/Tt) which is one of the control characteristics.

The. diall42 .for altering the setting .of the ,plug '96- of .the'valvewhich..-determines the auxiliary Itim'e Tncarries the index 161 whichworks in close-association with the scale. 162v carried on the dial .141which is conveniently calibrated in time units, for -example minutes,and a ceritainsetting of which, to bring the index 163 opposite thegraduation on the scale 164, corresponds to the condition-, .derivativetime equals zero. For this setting of. the dial 141 the integral time T1.is .indicateddirectly on the .dial .141 .by the index .161.

Should the derivative time and therefore .the value :of It not be zeroand the .dial .141 remain in the sameposition as beore,.the reading on.thedial 141 would indicate T2 and would-have to bev divided by 19) (.n)in order .to .obtainTi. Provisionhas, however, been-made for. obtaininga'directreadi ngof T1, thedial 141 being rotated by an corresponding tothe valve (Ifb (.n) as'indicated by the cooperationof .the index 163 onthe dial 14.1 with thmfixedsoale 164wh-ich carriesvalues of (n).

In order to .alter the proportional band, the potentiometer with. alogarithmic characteristic (which vis-containedinthe case 148) is set.by knob 155;, index 15.7 reading. against the fixed scale .158.Compensation for 4: (,n), is effected by rotating the case 148, thisbeing automatically eiiected, by means of the gearing 150', 151,, whenthe dial 141 is adjusted;

The procedure is setting the controller to the characteristic valuesK,T1 and (n) is as follows:

The valve controlling elements 144 and 142 are uncoupledand the knob 144for adjusting the value of Tris settin relation to the dial 142 forcontrolling the-valve for adjusting the value of T2, the adjustment ofthe knob in relation to the dial being efiectedin accordance-with thedesired value of (n). 'Thereupon the knob .144 and dial-14% are coupledtogether and the dial 141is-setin relationto the fixed scale 164 inorder to select the required value or (n). Thereafter the knob .144anddial 142 are adjusted together so that the required. integral time'T-Iiislindicated on the scale 162 on the dial 141. Finally, theproportionalband value K'is set by adjusting the index 157 on theattenuation setting means in relation to the scale 158.

Temperature compensation is achieved according to this invention in thefollowing manner.

The rotary motion of the setting knob and dial of the valves forcontrolling the settings T1 and T2 are conv'erted by the face cammechanism into a proportionate linear motion of the plugs 96 and 96'.Between the plug member proper (96 or 96') and the ball (112 or 112)moved linearly by the face cam mechanism, is interposed the body ofliquid contained in the recess (108 or 108) in the head (101 or 101),this liquid expanding with rise in temperature.

The liquid is so chosen that for a given temperature change, it willalter the linear adjustment of the respective plug 96 or 96' to the sameextent as the viscosity of the hydraulic liquid in the controller willhave been altered by the same change in temperature.

Fig. 8 illustrates an alternative arrangement of dials. The knob 144here carries a scale 165 instead of the index 159 of Fig. 5, andco-operates with an index 166 on the dial 142 (instead of a scale 160)this reading giving again the integral time T1. If the value of thederivative time To is required to be read directly, an additional indexring 167 is provided having a scale 168 calibrated in values of (n) andco-operating with a fixed index 169 while itself carrying a furtherindex 170 against which Tn can be read on the scale 165 secured to theknob 144.

Other arrangements of dials are possible, based on the construction ofthe valves to open according to a logarithmic law, and on the functionalrelationships and Logarithmic valve motions can be obtained either byappropriately forming the orifices of the valves, or by utilising valveshaving orifices or normal configuration,

amen

. T14. i. e.,, cylindrical, -conica1,orftheflike, with means interposedin the actuating mechanism for introducin'g a logarithmic correction.

1. In a three-term pneumatic controller-of the type nescribed, a firstfluid resistance, a second fluid resistance, a potentiometer resistance,"first means for varying "the first fluid resistance, logarithmally,second means for varying the second fluid resistance logarithmally,third means for coupling said ffirs't andksecond means for maintainingthe ratio of said first and second resistances at a selected value,fourth means for varying the potentiometer resistance logarithmally, and.fi'fth meansifor further varying said potentiometerresistance by avalue which is a function of said selected value of said ratio.

'2. In a three-term pneumatic controller of the type described, a lfirstfluid resistance, a secondfluid resistance, a further resistancecomprising a. potentiometer coil rotatably mounted on saidcont'roller, arotary wiper arm for saidv coil, :the logarithm of resistance of saidfurther resistance varying, directly in proportion 'tothe angularturning movement of said wiper arm and said coil relative to each other,"first means for varying. the first fluidresistance logarithmally,second means for varying the' second ifluid resistance :lbgarithmally,"third means for coupling saidfirst' and second means for maintaining.the ratio of saidfirst and second resistances at a selected value, forangularlyfturn'ing said coil relative to said wiper 'a'rmifor varying.said further resistance in accordance with the selectedvalue of saidratio, and fifth means for angulaily turningsaidwiper arm relative tosaid coil .for further varying. said further resistance.

3.In a three-term pneumatic controller of the type described, a firstfluid resistance, a second one resistance, a further resistancecomprising a potentiometer coil rotatably mounted on "said controller, arotary wiper arm for said coil, the logarithm of resistance ofsaid'further'resistance-varying directly "mproportion to'the angularturning'movement of saidwiperann and said coil relative to each'i'other,first means for varying thefirst fluid resistance logarithmally, secondmeans for varying the second fluid resistance logarithmally, third meansfor coupling said first and second means for maintaining the ratio ofsaid first and second resistances constant at a selected value andfourth means for angularly turning said coil relative to said wiper armfor varying said further resistance in accordance with said selectedvalue of said ratio.

4. In a three-term pneumatic controller of the type described, a firstfluid resistance, a second fluid resistance, a further resistancecomprising a potentiometer coil having a housing rotatably mounted onsaid controller, a first element mounted on said controller so as to belongitudinally movable and positioned and operative with respect to saidfirst fluid resistance for varying the resistance thereof by movement ofsaid first element, a second element mounted on said controller so as tobe longitudinally movable and positioned and operative with respect tosaid second fluid resistance for varying the resistance thereof bymovement of said second movable element, a longitudinal sleeve rotatablymounted on said controller, a shaft extending turnably through theopening of said sleeve, cam means coupling said shaft to said firstelement for producing movement thereof by turning of said shaft, thelogarithm of said resistance of said first fluid resistance varyingdirectly in proportion to the angular turning movement of said shaft,further cam means coupling said sleeve to said second element forproducing movement thereof by turning of said sleeve, the logarithm ofresistance of said second fluid resistance varying directly inproportion to the angular movement of said sleeve, means for couplingsaid shaft and said sleeve for maintaining the ratio of said first andsecond resistances constant at a selected value, a further shaftrotatably mounted on said controller, a potentiometer wiper arm coupledto said further shaft and positioned and operative with respect to saidcoil for varying the resistance thereof by rotary movement of saidfurther shaft, the logarithm of the resistance of said furtherresistance varying directly in proportion to the angular movement ofsaid further shaft relative to said coil, and means for rotating saidhousing for varying said further resistance in accordance with theselected value of said ratio.

5. A controller in accordance with claim 4, wherein said means forrotating said housing comprises an annular disc mounted coaxially withrespect to said firstmentioned shaft and drive means coupling said discand said housing so as to be adapted to drive said housing in adirection of rotation which is opposite to the direction of rotation ofsaid disc.

6. A controller in accordance with claim 4, said first and secondelements being respectively located rearwardly of said sleeve and saidfirst-mentioned shaft, said first and second elements being laterallyspaced, said firstmentioned shaft and said sleeve being locatedlaterally between said first and second movable elements, said furthercam means comprising an annular cam-supporting disc mounted on the rearend of said sleeve and concentric therewith, an outer face cam mountedon the rear face of said cam-supporting disc adjacent the outerperiphery thereof, and a ball bearing rotatably carried by the front endof said second movable element in operative contact with said outer facecam, said first-mentioned cam means comprising a further cam-supportingdisc mounted on the rear end of said first-mentioned shaft rearwardly ofsaid annular cam-supporting disc, an inner face cam mounted on the rearface of said further camsupporting disc adjacent the outer peripherythereof and inwardly of said inner face cam, and a further ball bearingrotatably carried by the front end of said first movable element inoperative contact with said inner face cam.

7. A controller in accordance with claim 6, wherein said means forrotating said housing comprises an annular disc mounted coaxially withrespect to said first- 16 mentioned shaft and drive means coupling saiddisc and said housing so as to be adapted to drive said housing in adirection of rotation which is opposite to the direction of rotation ofsaid disc.

8. Pneumatic control apparatus of the character which when supplied withan incoming signal proportional to the extent to which the value of avariable has departed from a required value will yield a pneumaticoutgoing signal composed of three components respectively proportionalto the magnitude, the time derivative and the time integral of theincoming signal, said apparatus comprising a first fluid resistance, asecond fluid resistance, a potentiometer resistance, first means forvarying the first fluid resistance logarithmally, second means forvarying the second fluid resistance logarithmally, third means forcoupling said first and second means for simultaneously varying saidfirst and second resistances whilst maintaining the ratio of the firstand second resistances constant at a selected value which is a functionof the ratio of said time derivative and said time integral, fourthmeans for varying the potentiometer resistance logarithmally inaccordance with the selected value of said ratio, and fifth means forfurther varying the potentiometer resistance to select theproportionality of said incoming signal to the extent to which the valueof said variable has departed from said required value.

References Cited in the file of this patent UNITED STATES PATENTS1,678,459 Bowland July 24, 1928 2,125,081 Moore July 26, 1938 2,266,871Krogh Dec. 23, 1941 2,285,540 Stein June 9, 1942 2,325,967 Moore Aug. 3,1943 2,360,889 Philbrick Oct. 24, 1944 2,372,345 Temple Mar. 27, 19452,374,336 DArcey Apr. 24, 1945 2,507,606 McLeod May 16, 1950 2,698,023Eckman Dec. 28, 1954

